There exists a need for topical ophthalmic pharmaceutical products to effectively treat allergic conjunctivitis, a disorder that presents with both acute allergic symptoms (i.e., seasonal allergy) and late phase inflammatory reactions (i.e., chronic, refractory or persistent allergy), as well as allergic rhinoconjunctivitis. It has been estimated that 46% (˜70 million) of the adult allergy patients in the United States suffer from both the acute and late phase conditions of allergic conjunctivitis, whereas only 19% suffer from only acute or late phase allergy, respectively. It is estimated that allergic rhinoconjunctivitis (a combination of ocular and nasal symptoms) may occur in up to 90% of patients with allergies. The average age of allergy sufferers—between 20 and 40 years—coincides with the average age of the work force and the most productive period of an individual's life.
Both seasonal and perennial allergic conjunctivitis (ocular allergies) are characterized by itchy, red, swollen, and watery eyes. Allergic rhinitis (nasal allergies) manifests as a runny nose, sneezing, congestion, and similar symptoms. It can be difficult for a physician to distinguish allergic conjunctivitis from allergic rhinoconjunctivitis because both allergic reactions can occur simultaneously or be triggered by the same types of stimuli. It is further difficult to distinguish acute allergic symptoms from late phase symptoms of allergic conjunctivitis, as each of these conditions can persist simultaneously or morph back and forth in any given individual. The signs and symptoms of allergic conjunctivitis and allergic rhinoconjunctivitis can significantly impact the quality of life of patients, from social interactions, productivity at work and school, to the ability to perform visual tasks such as working on a computer or reading.
Acute symptoms of allergic conjunctivitis are characterized by the clinical signs and symptoms of eye itching, redness, and swelling. Late phase or allergic inflammation reactions of allergic conjunctivitis include redness, lid swelling and tearing, and in some cases itching, as well as the predominance of congestion in the nose. Acute allergic symptoms are predominantly caused by the activation of mast cells, which when stimulated by an allergen (pollen, dust, dander) releases a host of substances that produce the signs and symptoms of allergic conjunctivitis (itching, redness, swelling, and tearing). Histamine is the primary mediator released and stimulates receptors on nerve endings and blood vessels to produce itching and redness. There are two histamine receptors that have been identified on the ocular surface. H1 receptors on nerve endings lead to itching, and H1 and H2 receptors on blood vessels lead to dilation of the blood vessels, leading to redness, and leakage of fluid from the vessels into the surrounding tissue producing swelling. Late phase inflammatory reactions are mediated by activation of inflammatory cells.
Like allergic conjunctivitis, allergic rhinoconjunctivitis is an allergen-induced, mast cell-mediated response. The reaction is triggered when airborne allergens bind to antibodies attached to the surface of mast cells in the eye and/or nose. Mast cells, in turn, release chemical mediators, which account for the immediate reaction in sensitized individuals exposed to allergen. Some of these mediators, such as histamine, directly affect blood vessels and nerves, leading to the signs and symptoms of allergic disease. Other released mediators cause the influx of white blood cells to the site, which leads to sustained symptoms in severe cases and particularly congestion in the nose.
Allergic conjunctivitis and rhinoconjunctivitis may also co-exist with other external ocular conditions and diseases, such as dry eye, or irritations caused by pollutants or other causes. This leads to a compromised tear film, which serves to protect the ocular surface from allergens.
Currently available treatments for eye allergy include: drops which can wash allergens off the ocular surface and act as a barrier for the eye (e.g. artificial tears), drugs which block histamine from binding to the histamine receptors (e.g. antihistamines), drugs that block the release of histamine and other substances from the mast cell (e.g. mast cell stabilizers), drugs with multiple modes of action (e.g. antihistamine/mast cell stabilizing agents), and drugs that can actively constrict blood vessels thus reducing redness and swelling (e.g. vasoconstrictors). The criteria which may be considered in evaluating the appropriateness of an agent for a patient include: efficacy at onset of action, duration of action, how well it controls the individual signs and symptoms of allergic conjunctivitis, comfort of the formulation when instilled in the eye, and safety of the formulation when instilled in the eye. The comfort of an ophthalmic product depends on the active pharmaceutical ingredient itself, as well as the nature of the formulation and the vehicle that makes up the product. Oral antihistamines have been shown to induce decreased tear production and lead to dryness of the ocular surface, which can exacerbate ocular discomfort and can make the eye susceptible to irritation by an ophthalmic product.
The currently available treatments which contain a single active agent, such as an antihistamine or a mast cell stabilizer, typically provide relief for only acute allergic conjunctivitis and don't address the signs and symptoms of the late phase inflammatory reactions (i.e., chronic, refractory, or persistent allergy).
Currently available treatments for allergic rhinoconjunctivitis include eyedrops, nasal sprays, and systemic oral agents. Currently approved anti-allergy eyedrops are indicated for ocular allergy and nasal sprays are targeted for nasal allergy. Systemic agents, while they have indications to treat both nasal and ocular symptoms, several well controlled clinical trials conducted to ophthalmic standards have shown that systemic antihistamines are inferior to eyedrops in treating the ocular signs and symptoms (Spangler et al., Clin. Ther. 25(8), 2245-2267 (2003), are not in fact clinically effective on eye allergy, and actually have been shown by objective measures to reduce tear production on the eye by 50%, causing ocular dryness (Ousler et al, Ann Allergy Asthma Immunol. November; 93(5):460-4 (2004)). Further studies have shown that the combination of an eyedrop and nasal steroid is more effective than a systemic agent in treating the ocular and nasal signs and symptoms of allergy (Lanier et al. Clin. Ther. 24(7), 1161-1174 (2002)).
Cetirizine hydrochloride is a racemic selective H1 receptor inverse agonist which functions as an antihistamine. It is a major metabolite of hydroxyzine and a derivative of piperazine. The levorotary enantiomer of cetirizine is known as levocetirizine. Cetirizine hydrochloride is FDA approved for oral use and is used as a systemic antihistamine for the treatment of allergies, hay fever, angioedema, and urticaria. It has been historically difficult to prepare cetirizine as an ophthalmic solution with satisfactory safety and stability profiles. Cetirizine has the disadvantage of forming aggregates in solution at low concentrations (typically less than 1% (w/v)), thereby decreasing the stability as an aqueous solution. Moreover, higher concentrations of cetirizine (1% and above) are strongly irritating and thus unsuitable for direct ocular or nasal administration. U.S. Pat. No. 5,419,898 addresses these issues by using a cyclodextrin compound to increase the solubility and stability of cetirizine for ophthalmic use. However, a cyclodextrin-free stable ophthalmic formulation containing cetirizine as the only active ingredient that is both comfortable in the eye and effective to mitigate the symptoms of allergic conjunctivitis has never been previously achieved.
There thus exists a need to develop an effective, stable yet comfortable and safe cetirizine formulations for ophthalmic administration for the treatment of allergic conjunctivitis (i.e., the acute phase, the late inflammatory phase, or both) and allergic rhinoconjunctivitis. Such formulations for administration directly to the eye would be advantageous over systemic oral formulations and nasal sprays due to faster action and avoidance of the side effects associated with systemic administration.